Heretofore, many pressure-sensitive adhesive sheets produced by integrally laminating a pressure-sensitive adhesive layer to one face of a sheet-like base made of a synthetic resin sheet have been proposed. These pressure-sensitive adhesive sheets are required to have various qualities depending upon their applications, and pressure-sensitive adhesive layers to be used for surface decoration are required to have a high design effect in color, decoration, and so on because they are to be used for exterior decoration of walls of buildings and surfaces of furniture, fixtures, and the like.
When a pressure-sensitive adhesive sheet is stuck to the surface of an object, the pressure-sensitive adhesive layer is pressed against the surface of the object from an arbitrary edge of the sheet by using a sticking tool such as a squeegee, and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is stuck to the object gradually.
However, there is a problem that air enters into between the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet and the surface of the object facing the pressure-sensitive adhesive layer to form an air pocket and this air pocket causes irregularities in the surface of the pressure-sensitive adhesive sheet for surface decoration, resulting in deterioration in exterior appearance of the pressure-sensitive adhesive sheet stuck to the object.
Patent document 1 proposes forming lattice-like groove portions in the surface of a pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet and discharging, through the grooves, air that has entered into between the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet and the surface of an object facing the pressure-sensitive adhesive layer.
As to the lattice-like groove portions, a plurality of groove portions parallel to each other have been formed at fixed intervals and a plurality of groove portions perpendicular to those groove portions have been formed parallel to each other at fixed intervals. The pitch between the groove portions is limited to about 400 μm or less.
Since the pitch between the groove portions is very small as about 400 μm or less, projecting portions formed between the groove portions are also very small. On the other hand, in sticking the pressure-sensitive adhesive sheet to the surface of an object, when a sticking tool is pressed against the surface of the pressure-sensitive adhesive sheet, the pressure from the sticking tool is received by projecting portions formed between the groove portions. Since the projecting portions are very small, there is a problem that the projecting portions are deformed easily by the pressure applied by the sticking tool, so that irregularities are formed on the surface of the pressure-sensitive adhesive sheet, resulting in deterioration in the external appearance of the pressure-sensitive adhesive sheet.
Under such a situation, one probable solution is to increase the pitch between groove portions. However, when the pitch between the groove portions is excessively large, there was a problem that when air is captured between projecting portions formed between the grooves and the surface of an object facing the projecting portions, it is impossible to lead the air smoothly to the groove portions and the air is trapped between the projecting portions and the facing surface of the object facing the projecting portions.
Moreover, human eyes have a property of particularly easily recognizing objects regularly formed. As to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which groove portions have been formed in a lattice-like form regularly at a small pitch, the groove portions were easily recognized visually through the sheet-like base of the pressure-sensitive adhesive sheet. Therefore, there was a problem that drawing patterns, such as decorative patterns or letters, printed on the surface of the sheet-like base of a pressure-sensitive adhesive sheet are damaged by the groove portions.
Patent document 2 discloses a pressure-sensitive adhesive processing film including a pressure-sensitive adhesive film body and a pressure-sensitive adhesive layer integrally laminated on one side of the pressure-sensitive adhesive film body, wherein thin groove portions have been formed on the adhesive surface of the pressure-sensitive adhesive layer. As to the formation pattern of the groove portions, a lattice-like form, a wavy line form, a zigzag line form, and so on are proposed.
However, since the aforesaid groove portions have been formed regularly from a prescribed form repeated at a fixed period, there was a problem that the groove portions are easily recognized by human eyes as described above and the groove portions are recognized through the pressure-sensitive adhesive film body, so that decorative patterns and the like printed on the surface of the pressure-sensitive adhesive film body are damaged by the groove portions.
Moreover, patent document 3 discloses an article with an adhesive composed of a polymer film and a pressure-sensitive adhesive, wherein prescribed grooves have been formed on the surface of the pressure-sensitive adhesive. It is disclosed that the groove portions may be provided either in a regular pattern or in a random pattern (paragraph [0009]).
However, there was a problem that if grooves are provided in a regular pattern as described above, a decorative pattern or the like printed on the surface of the polymer film body will be damaged by the grooves. Although there is a disclosure that groove portions may be provided in a random pattern, no specific pattern of groove portions is disclosed and there was a problem that air taken into between the pressure-sensitive adhesive and an object cannot be discharged well through groove portions by only forming the groove portions randomly. Moreover, the groove portions are visually recognized through the polymer film, so that the same problem as that described above has arisen.
Patent document 1: WO 2003/025078
Patent document 2: JP 7-138541 A
Patent document 3: Japan Patent No. 3550096